Fluorescent Chemo-Sensor for Metal Cations Based on Thiacalix[4]arenes Modi®ed with Dansyl Moieties at the Lower Rim Yutaka Higuchi, a Miyuki Narita, a Tomohiro Niimi, a Nobuaki Ogawa, a Fumio Hamada, a, * Hitoshi Kumagai, b Nobuhiko Iki, c Sotaro Miyano c, * and Chizuko Kabuto d a Department of Materials-Process Engineering and Applied Chemistry for Environments, Faculty of Engineering and Resource Science, Akita University, Tegata, Akita 010-8502, Japan b Chemical Technology Laboratory, Cosmo Research Institute, Chemical Technology Laboratory, 1134-2 Gongendo, Satte, Saitama 340-0193, Japan c Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Aramaki-Aoba 07, Aoba-ku, Sendai 980-8579, Japan d Department of Chemistry, Graduate School of Science, Tohoku University, Aoba, Aoba-ku, Sendai 980-8579, Japan Received 27 March 2000; accepted 1 May 2000 Abstract ÐThe selective de-tert-butylation of p-tert-butyl thiacalix[4]arene (p-tert-butyl TCA) with AlCl 3 at 808C has been investigated. Mono-, di-, and tri-p-tert-butyl thiacalix[4]arene (mono-, di- and tri-TCA, respectively) were obtained in yields of 6.5, 20 and 21%, respectively, when p-tert-butyl TCA was treated with 7.1 equiv. of AlCl 3 for 30 min. De-tert-butyl TCA (TCA) was exclusively obtained when 10.5 equiv. of AlCl 3 was used. These derivatives are converted to ¯uorescent active derivatives by modi®cation with dansyl moiety at the lower rim, which are used as metal sensors in aqueous solution. The extent of the ¯uorescent variations with the metal cations was used to display the sensing factors, DI/I 0 . These hosts show much higher sensitivity for transition metal cations such as Co 21 , Ni 21 , and Cd 21 than those of alkali metal cations such as Li 1 , Na 1 , and K 1 . The effect of p-tert-butyl groups on metal sensing ability of these hosts was studied. It was found that p-tert-butyl groups decrease the sensing ability of these hosts. It is the ®rst example to show that water soluble TCA derivatives can detect metal cations directly in aqueous solution by variation of ¯uorescence intensity upon addition of a metal cation. q 2000 Elsevier Science Ltd. All rights reserved. Introduction Fluorescent metal sensing by calixarene derivatives has been investigated by a couple of groups. 1 The molecular design was carried out by introduction of ligand and ¯uorescent active moiety on the upper or lower rim of calixarenes, because calixarene itself can hardly make a host±guest complexation with metal cations. On the other hand, thiacalix[4]arene (TCA) is composed of benzene rings, linked via sul®de bridges, which itself can make host-guest complexation with metal cations because the sul- ®de functional group has af®nity for metal cations. Recently, a practical synthetic method of thiacalixarene has been reported by Kumagai et al. 2 Thus, a couple of TCA derivatives, such as thiacalix[4]arene-tetrasulfonate, tetra-O-alkylated at the lower rim of thiacalix[4]arene, sul- fone-thiacalix[4]arene, and a chirally modi®ed p-tert-butyl thiacalix[4]arene have been prepared to expand the func- tions of TCA. 3 In a previous paper, we ®rst reported a metal sensor system based on water soluble di- and tri- dansyl modi®ed p-tert-butyl TCA, (tetra-TCA-2 and tetra- TCA-3, respectively) (Scheme 1). 4 These compounds show the highest sensitivity for Cd 21 . As a further extension of the work, we synthesized nine new analogues of the TCA with dansyl moieties. We also investigate the effect of tert-butyl groups on the metal sensing ability of dansyl modi®ed thia- calix[4]arene, because we succeeded in effecting selective removal of p-tert-butyl groups of p-tert-butyl TCA. Among Tetrahedron 56 (2000) 4659±4666 Pergamon TETRAHEDRON 0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved. PII: S0040-4020(00)00377-X Scheme 1. The structure of dansyl modi®ed TCA analogues. Keywords: p-tert-butyl thiacalix[4]arenes; tri-TCA; dansyl moiety. * Corresponding authors. Tel.: 181-18-889-2440; fax: 181-18-837-0404; e-mail: hamada@ipc.akita-u.ac.jp